The germ theory of disease is developed and begins to be applied to drug therapy, surgery, and public health.

The ideas that become germ theory gradually evolved over time, with the concept of "seeds of disease" that can spread between people's bodies showing up as early as the 16th century. About 100 years later, the microscope was invented, thereby enabling people to see microorganisms. This awareness of microbiology then led to the development of the understanding over the following century that "germs" cause illness.

As this becomes the primary belief system within medicine, most care strategies focus on killing the germs, which leads to a pharmaceutical approach, rather than attending to the social and environmental contexts that create the conditions for illness. Unfortunately, rather than examining all of these factors as elements that can cause illness, Western medicine moves almost completely towards the science of germs and germ eradication in this era.